Power of tungsten alloy with transition metal dissolved therein as solid solution and process for producing the same

ABSTRACT

This invention is related to a powder of a tungsten alloy with a transition metal dissolved therein as a solid solution that is suitable as material for a cemented carbide represented by formula [1] and a material for a catalyst. The powder of tungsten alloy is characterized in that at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel is dissolved as a solid solution in a tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram. Formula [1]: M−W wherein M represents one or more elements selected from Co, Fe, Mn and Ni. The use of tungsten alloy powder can provide a tungsten carbide with a transition metal dissolved therein as a solid solution in which a solid solution phase comprising at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel, tungsten and carbon is included in a tungsten carbide skeleton, and a tungsten carbide diffused cemented carbide.

TECHNICAL FIELD

The present invention relates to a tungsten alloy powder with a transition metal dissolved therein as a solid solution and a process for producing the same.

BACKGROUND ART

Tungsten has a high melting point and modulus of elasticity and is useful as a filament material or a raw material for tungsten carbide (WC). However, the price of tungsten is showing a tendency to increase sharply in accordance with a rapid increase in the domestic demand of China, since the raw material thereof is present only in China. In order to develop materials capable of conserving tungsten resources, there is a need to replace a portion of tungsten with a transition metal element.

However, it is difficult to prepare tungsten by melting due to the high melting point thereof. Further, in spite of using powder metallurgy for imparting a form, there is a problem in that alloying is not performed in a blended elemental method of a tungsten powder and a transition metal element. In addition, it is difficult to apply an atomization method for preparing an alloy powder.

Meanwhile, a conventional method for preparing tungsten alloy powder by co-precipitating a metal salt or metal hydroxide is known (Patent Citation 1 and Patent Citation 2).

PATENT CITATION

-   Patent Citation 1: PCT Japanese Translation Patent Publication No.     2002-527626 -   Patent Citation 2: U.S. Pat. No. 4,913,731

DISCLOSURE OF INVENTION Technical Problem

However, in the preparation methods disclosed in Patent Citation 1 and 2, an alloy powder contains a phase of a transition metal element, in addition to a tungsten phase and a tungsten phase alloyed with a transition metal element, due to the operation of “co-precipitation”, and alloying is not sufficiently performed.

To solve the problem, an object of the present invention is to provide a novel tungsten alloy powder in which a transition metal element is dissolved (compulsorily dissolved) as a solid solution and a process for producing the same.

Technical Solution

As a result of a variety of extensive and intensive studies to accomplish the object, the present inventors discovered that when tungsten ions and ions of a transition metal are homogenized at an ionic level in an aqueous solution, subjected to drying by distillation or spray-drying, thermal decomposition and then hydrogen thermal reduction to obtain a tungsten powder, a tungsten alloy powder in which a transition metal element is thoroughly compulsorily dissolved as a solid solution can be prepared, and thus accomplished the present invention.

That is, the present invention provides a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula 1 in which at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in a tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram.

M−W  Formula 1

wherein M represents one or more selected from Co, Fe, Mn and Ni.

The tungsten alloy powder with a transition metal dissolved therein as a solid solution of the present invention can be exemplified by 1) a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Co—W in which cobalt is dissolved as a solid solution in a tungsten grating, 2) a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by the formula of Fe—W in which iron is dissolved as a solid solution in a tungsten grating, and 3) a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by the formula of Ni—W in which nickel is dissolved as a solid solution in a tungsten grating, all of in which a single transition metal is dissolved as a solid solution in tungsten.

The cobalt, iron and nickel portions may be partially substituted by another one or more transition metals selected from the group consisting of iron, manganese and nickel, thus making it possible to obtain a composite transition metal-dissolved tungsten powder. Of these, preferable are 4) a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula 2 of Co−M1−W (wherein, M1 represents one or more elements selected from Fe, Mn and Ni) in which cobalt is partially substituted by one or more selected from the group consisting of iron, manganese, iron-manganese and nickel, and 5) a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula 3 of Fe-M2-W (wherein, M2 represents one or more selected from Co, Mn and Ni) in which iron is dissolved as a solid solution in tungsten grating and iron is partially substituted by one or more selected from the group consisting of cobalt, manganese and nickel.

The amount of transition metal dissolved as a solid solution in tungsten may be up to an equivalent molar amount of tungsten. In the case where the dissolved element as a solid solution is cobalt, cobalt is preferably 40 to 10 mol % with respect to 60 to 90 mol % of tungsten and other transition metals are the same.

A second object of the present invention is to provide a process for producing the transition metal-dissolved tungsten powder, by mixing an aqueous solution containing tungsten ions with an aqueous solution containing at least ions of one transition metal selected from the group consisting of cobalt, iron, iron-manganese and nickel, wherein the mixing is performed such that the tungsten ions are 60 mol % or more and the transition metal ions are 40 mol % or less, drying the mixed aqueous solution by distillation or spraying, thermally decomposing the resulting solid, followed by hydrogen thermal reduction, to prepare a transition metal-dissolved tungsten alloy powder represented by Formula 1 of M−W (wherein M represents one or more selected from Co, Fe, Mn and Ni), in which a transition metal element is dissolved.

In the present invention, preferably, the aqueous solution containing tungsten ions is an ammonium paratungstate aqueous solution (5(NH₄)₂O.12WO₃.5H₂O) and the aqueous solution containing ions of at least one transition metal selected from the group consisting of cobalt, iron, manganese and nickel is a transition metal complex salt aqueous solution. Examples of useful transition metal complex salts include acetates (Fe(OH)(C₂H₃OO)₂, CO(C₂H₃O₃)₂.4H₂O, Mn(CH₃COO)₂.4H₂O, Ni(C₂H₃O₃)₂.xH₂O) and sulfates (FeSO₄.7H₂O, CoSO₄.7H₂O, NiSO₄.6 H₂O, MnSO₄.5H₂O).

Advantageous Effects

The tungsten alloy powder obtained from the present invention contains a transition metal element dissolved as a solid solution in a tungsten grating and exhibits the appearance of a peak derived from a bcc tungsten phase in an X-ray diffraction diagram. The tungsten alloy powder with a transition metal dissolved therein as a solid solution has a tungsten grain boundary in which a transition metal element or a metal compound thereof are not substantially present.

The tungsten alloy powder related to the present invention is a transition metal-dissolved tungsten alloy powder represented by Formula 1 of M−W (wherein M represents one or more selected from Co, Fe, Mn and Ni) wherein the alloy powder basically contains 0.3% by weight to 20.8% by weight of cobalt and the balance of tungsten, wherein cobalt is entirely or partially substituted by one or more elements of iron, manganese and nickel. When the tungsten alloy powder contains cobalt and the M component is present in an amount of less than 0.3% by weight of the tungsten alloy powder, resource saving effects cannot be obtained. When the M component exceeds 20.8% by weight, a second phase is precipitated on a tungsten grain boundary and a tungsten alloy powder in which the transition metal element is dissolved (compulsorily dissolved) as a solid solution is not obtained.

The cobalt is substituted and present at a lattice position of tungsten and acts as a replacement element for tungsten, thus being effective for the resource saving of tungsten whose price is sharply increasing. In addition, cobalt is dissolved (compulsorily dissolved) as a solid solution, thus improving catalytic activity and imparting catalytic functions to the alloy powder of the present invention.

Meanwhile, nickel has similar functions to cobalt and is cheaper than cobalt. In addition, nickel provides a higher catalytic activity than cobalt. Iron improves the strength of the tungsten powder and is cheap. In addition, iron and iron-manganese efficiently utilize their transformational properties and contribute to improvement of the fracture toughness of cemented carbide.

When a metal complex salt, such as acetates of iron, nickel, manganese and cobalt (Co(C₂H₃O₃)₂.4H₂O, Fe(OH)(C₂H₃OO)₂, Mn(CH₃COO)₂.4H₂O, Ni(C₂H₃O₃)₂.xH₂O) as the aqueous solution containing transition metal ions, it is soluble in water, does not produce harmful materials and is low in environmental load. In addition, use of transition metal sulfates of iron, nickel and cobalt (CoSO₄.7H₂O, FeSO₄.7H₂O, NiSO₄.6H₂O) is also effective in realizing circulation society. Generally, in an electrolytic refining process of copper, the transition metals of iron, nickel and cobalt are concentrated in sulfate in an electrolyte. Accordingly, waste liquid produced during the electrolytic refining of copper may be used as a raw material of the tungsten alloy powder of the present invention and the sulfate produced during drying by distillation or spray-drying may be efficiently used as a by-product.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described with reference to representative examples. However, using an ion metal complex salt alone or in combination of two or more kinds thereof, as the aqueous solution containing transition metal ions, it will be apparent to those skilled in the art from Examples that one or more transition metals can be dissolved as a solid solution in a tungsten metal, and the tungsten metals can be partially substituted.

Example 1

A conventional material (No. 1), materials of the present invention (Nos. 2 to 9) and Comparative materials (Nos. 10 and 11) were prepared to have the chemical components (mol %) shown in Table 1, and the possibility of a compulsive solid solution and the existence of precipitation of the second phase were confirmed by X-ray diffraction and EPMA.

TABLE 1 Chemical component (mol %) and formation of compulsive solid solution No Fe Co Mn Ni W Note 1 — 20 — — Bal Conventional Powder mixing Second phase (Co) material precipitation 2 — 10 — — Bal Material of the Solution method Compulsive solid present invention solution 3 — 20 — — Bal Material of the Solution method Compulsive solid present invention solution 4 — 30 — — Bal Material of the Solution method Compulsive solid present invention solution 5 — 40 — — Bal Material of the Solution method Compulsive solid present invention solution 6 10 10 — — Bal Material of the Solution method Compulsive solid present invention solution 7 15 8 1.5 20 Bal Material of the Solution method Compulsive solid present invention solution 8 — 10 — 10 Bal Material of the Solution method Compulsive solid present invention solution 9 5 10 — 1.85 Bal Material of the Solution method Compulsive solid present invention solution 10 — 90 — — Bal Comparative Solution method 2(Co₃W) phase material precipitation 11 — 50 — — Bal Comparative Solution method 2(Co₇W₆) phase material precipitation 12 0.1 19.9 — — Bal Material of the Solution method Compulsive solid present invention solution 13 5.0 15.0 — — Bal Material of the Solution method Compulsive solid present invention solution 14 20 — — — Bal Material of the Solution method Compulsive solid present invention solution 15 17.4 — 2.4 — Bal Material of the Solution method Compulsive solid present invention solution

In Table 1, the term “solution method” is a process of the present invention which includes mixing an aqueous solution of transition metal acetate (Co(C₂H₃O₃)₂.4H₂O, Fe(OH)(C₂H₃OO)₂, Mn(CH₃COO)₂.4H₂O and/or Ni(C₂H₃O₃)₂.xH₂O) with an aqueous solution of ammonium paratungstate (5(NH₄)₂O.12WO₃.5H₂O), subjecting the mixture to drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and subjecting the resulting product to hydrogen thermal reduction under a hydrogen gas at 1073 K for 1 h to obtain a tungsten alloy powder.

Sample No. 1 is a conventional material obtained using a blended elemental method, as a conventional powder metallurgy method, including weighing and mixing 7.42% by weight of a pure cobalt powder and the balance of a pure tungsten powder to make the chemical composition of Table 1, followed by compression molding at a pressure of 2 ton/cm², and maintaining for 1 h under a hydrogen gas at 1073 K. A pure cobalt phase remained as the second phase and alloying with tungsten was not performed.

Sample No. 2 is a material of the present invention obtained by a solution method. An aqueous solution of transition metal acetate (Co(C₂H₃O₃)₂.4H₂O) was mixed with ammonium paratungstate. In the X-ray diffraction diagram of the resulting alloy powder, only a peak derived from a bcc W phase appeared and a W alloy powder was obtained in which Co was homogenously compulsorily dissolved as a solid solution.

Sample No. 3 is a material of the present invention obtained by a solution method. An aqueous solution of a transition metal acetate Co(C₂H₃O₃)₂.4H₂O was mixed with ammonium paratungstate to make the composition 80 mol % W-20 mol % Co. In the X-ray diffraction diagram of the resulting alloy powder, only a peak derived from a bcc W phase appeared and a W alloy powder was obtained in which Co was homogenously compulsorily dissolved as a solid solution. The equilibrium phases of this composition at a hydrogen thermal reduction temperature of 1073 K were a W phase and a Co₇W₆ phase. First, it was confirmed that, when cobalt ions and tungsten ions in an aqueous solution were made homogeneous at an ion level by the solution method, cobalt was captured in a tungsten grating even after the hydrogen thermal reduction and equilibrium phase of Co₇W₆ could not be formed. That is, it was discovered that, when a solution method is applied, an alloy powder compulsorily dissolved as a solid solution in a non-equilibrium state can be prepared.

Samples No. 4 and No. 5 are materials of the present invention obtained by a solution method. It was confirmed that a W alloy powder in which Co was homogenously compulsorily dissolved in a non-equilibrium state to make a composition of 60 mol % W-40 mol % Co could be obtained. When the solution method was applied, compulsorily dissolved alloy powder as a solid solution in a non-equilibrium state could be prepared, without forming an equilibrium phase of Co₇W₆ to make this composition.

Sample No. 6 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution is partially substituted by an Fe(OH)(C₂H₃OO)₂ aqueous solution. It was discovered that compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Fe.

Sample No. 7 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution is partially substituted by an aqueous solution of Fe(OH)(C₂H₃OO)₂, Mn(CH₃COO)₂.4H₂O and Ni(C₂H₃O₃)₂.xH₂O. It was discovered that a compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Fe, Mn or Ni.

Sample No. 8 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution is partially substituted by an aqueous solution of Ni(C₂H₃O₃)₂.xH₂O. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Ni.

Sample No. 9 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution is partially substituted by an aqueous solution of Fe(OH)(C₂H₃OO)₂ and Ni(C₂H₃O₃)₂.xH₂O. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Fe and Ni.

Sample No. 10 is a Comparative material obtained by the solution method. In this composition of 10 mol % W-90 mol % Co, an equilibrium phase of Co₃W was finally precipitated as a second phase. Accordingly, when the amount of Co is greater, W atoms are readily diffused in a Co lattice in spite of using a solution method and thus a compulsory solid solution could not be prepared.

Sample No. 11 is a Comparative material obtained by a solution method. In this composition of 50 mol % W-50 mol % Co, the equilibrium phase of Co₇W₆ was finally precipitated as the second phase. Accordingly, W atoms were also diffused in this composition, and a compulsory solid solution could not be thus prepared.

Sample No. 12 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution was partially substituted by an Fe(OH)(C₂H₃OO)₂ aqueous solution. Sample No. 12 is a compulsorily dissolved alloy powder as a solid solution in which Co was partially substituted by a small amount of Fe.

Sample No. 13 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution was partially substituted by an Fe(OH)(C₂H₃OO)₂ aqueous solution. A compulsorily dissolved alloy powder as a solution solid could be prepared, although an Ni(C₂H₃O₃)₂.xH₂O aqueous solution shown in Sample No. 8 was not added.

Sample No. 14 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution was entirely substituted by an Fe(OH)(C₂H₃OO)₂ aqueous solution. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was entirely substituted by Fe.

Sample No. 15 is a material of the present invention obtained by a solution method, in which a Co(C₂H₃O₃)₂.4H₂O aqueous solution was entirely substituted by an Fe(OH)(C₂H₃OO)₂ aqueous solution and a Mn(CH₃COO)₂4₂H₂O aqueous solution. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was entirely substituted by Fe and Mn.

Tungsten Carbide Preparation Example

A conventional material (No. 21), materials of the present invention (Nos. 22 to 28, and Nos. 31 to 34) and Comparative materials (Nos. 29 and 30) having chemical components (wt %) shown in Table 2 were prepared.

TABLE 2 Chemical components of tungsten carbide (wt %) and formation of metal phase or second carbide phase in the carbide No Fe Co Mn Ni W C Note 21 — — — Bal 6.13 Conventional material X 22 — 1.20 — Bal 6.10 Material of the ◯ present invention 23 — 7.00 — Bal 5.70 Material of the ◯ present invention 24 — 16.71 — Bal 5.11 Material of the ◯ present invention 25 — 19.70 — Bal 4.20 Material of the ◯ present invention 26 3.32 3.50 — Bal 5.91 Material of the ◯ present invention 27 5.00 3.00 0.5  10.0 Bal 5.11 Material of the ◯ present invention 28 — 3.50 3.48 Bal 5.91 Material of the ◯ present invention 29 — 19.76 — Bal 4.19 Comparative material X 30 — 0.29 — Bal 6.12 Comparative material X 31 0.033 6.96 — — Bal 5.70 Material of the present invention 32 1.66 5.25 — — Bal 5.71 Material of the ◯ present invention 33 6.65 — — — Bal 5.72 Material of the ◯ present invention 34 5.79 — 0.79 — Bal 5.73 Material of the ◯ present invention Metal phase is formed in carbide ◯ Metal phase is not formed in carbide X

The materials of the present invention of Nos. 22 to 27 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which a transition metal was compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, a tungsten alloy powder in which a transition metal element was compulsorily dissolved as a solid solution was prepared, by mixing an aqueous solution of transition metal acetate (CO(C₂H₃O₃)₂.4H₂O, Fe (OH)(C₂H₃OO)₂, Mn (CH₃COO)₂.4H₂O and/or Ni(C₂H₃O₃)₂.xH₂O) with an aqueous solution of ammonium paratungstate (5(NH₄)₂O.12WO₃.5H₂O), drying by distillation (or spray drying), thermally decomposing the resulting solid with oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under a hydrogen gas at 1073 K.

Then, this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide.

Sample No. 21 was WC carbide obtained by mixing WO₃ with graphite and carbonizing at 1473 K for 1 h in accordance with a conventional powder metallurgy method. A metal phase was not present in the WC skeleton.

Sample No. 22, Sample No. 23, Sample No. 24, Sample No. 25, Sample No. 26, and Samples Nos. 27 and 28 are materials of the present invention obtained by a solution method and carbonization. A specific structure in which a metal phase is present in the WC skeleton was obtained. This metal phase contributes to resource saving of tungsten and the improvement of mechanical properties of carbide. It was confirmed that the content of metal phase increases in accordance in the order of Sample No. 22, Sample No. 23, Sample No. 24 and Sample No. 25.

Sample No. 26, Sample No. 27 and Sample No. 28 are carbides in which metal phase cobalt present therein is substituted by iron, iron-manganese and nickel, respectively, to reduce the cost.

Samples Nos. 29 and 30 are Comparative materials obtained by a solution method and carbonization. When the amount of cobalt is greater than that of tungsten as in Sample No. 29, tungsten is diffused in the cobalt in the process of preparing the tungsten alloy powder, to produce an equilibrium phase of Co₃W or Co₇W₆. As a result, when this alloy powder is carbonized, the metal phase surrounds the carbide and the metal phase cannot be thus present in the carbide.

The materials of the present invention of Nos. 31 and 32 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which a transition metal is compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, in the same manner as in Sample 26, a tungsten alloy powder in which a transition metal element is compulsorily dissolved as a solid solution was prepared, by mixing an aqueous transition metal acetate solution (Co(C₂H₃O₃)₂.4H₂O) and an aqueous solution of Fe(OH)(C₂H₃OO)₂ with an aqueous solution of ammonium paratungstate (5(NH₄)₂O.12WO₃.5H₂O), drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under hydrogen gas at 1073 K. Then, this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide. A specific structure in which a Co—Fe solid solution phase is present in the WC skeleton was obtained.

The materials of the present invention of Nos. 33 and 34 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which Fe and Mn were compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, the tungsten alloy powder in which a transition metal element is compulsorily dissolved as a solid solution was prepared, by mixing an aqueous solution of (Fe(OH)(C₂H₃OO)₂) and an aqueous solution of Mn(CH₃COO)₂.4H₂O with an aqueous solution of ammonium paratungstate (5(NH₄)₂O.12WO₃.5H₂O), drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under hydrogen gas at 1073 K. Then, this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide. When Co is entirely substituted by Fe or Fe and Mn, WC containing a Fe metal or Fe—Mn solid solution could be obtained.

FIG. 1 shows EPMA observation results of the material of the present invention of Sample No. 23. As can be seen from the X-ray image of W and C corresponding to the SEM image, the structure of WC was formed. In addition, it was found from the X-ray image of Co that a metal phase was formed in the structure of WC. That is,

(a) is an SEM image. A white part represents a WC skeleton and a black part represents a domain composed of a Co metal. The Co domain is inevitably grown when sintered at 1623K at 3.6 ks, but is maintained at 3 mm or less.

(b) represents an X-ray image of W and shows formation of the WC skeleton.

(c) represents an X-ray image of Co and shows formation of the Co domain in a WC skeleton.

(d) represents an X-ray image of C and shows formation of the WC skeleton.

This formation of metal phase is effective in reducing the amount of tungsten used and improves mechanical properties. Accordingly, a cemented carbide, in which this novel WC carbide is dispersed, is suitable as an abrasion resistance material.

The cemented carbide may be prepared by sintering tungsten carbide of the present invention with a Co powder in accordance with a known preparation method. FIG. 2 shows an EPMA image of a cemented carbide, experimentally prepared by adding 5% by weight of bonded Co to the material of the present invention of Sample No. 34 and sintering at 1623 K at 3.6 ks. It can be seen that, in the cemented carbide, a Fe—Mn solid solution is formed in the WC skeleton and a bonded Co is partially distributed in this Fe—Mn solid solution during sintering. The Vickers hardness was an extremely high hardness of Hv1945. Further, it could be observed that a tip of a Vickers hardness test indentation did not crack and exhibited excellent toughness. That is,

(a) is an SEM image. A white part is a WC skeleton and a black part is a domain composed,of a Fe—Mn solid solution. When sintered, the metal domain inevitably grows, but is maintained at 1 mm or less. This SEM image exhibits an indentation of a Vickers hardness test. The Vickers hardness was an extremely high hardness of Hv1945. Further, it can be seen that a tip of a Vickers hardness test indentation did not crack and exhibited excellent toughness.

(b) represents an X-ray image of W and shows formation of the WC skeleton. In addition, a part of W is distributed in the Fe—Mn solid solution domain.

(c) represents formation of the Fe—Mn solid solution domain, which is an X-ray image of Fe.

(d) is an X-ray image of Co. The bonded Co is partially distributed in the Fe—Mn solid solution domain during sintering.

(e) represents an X-ray image of C and shows formation of a WC skeleton.

(f) represents an X-ray image of Mn and shows formation of a Fe—Mn solid solution domain.

The reason why the WC carbide including a metal domain exhibits a high hardness is that in the present invention, the WC skeleton successfully creates a micro structure which constrains deformation of the metal domain.

INDUSTRIAL APPLICABILITY

As apparent from the foregoing, the alloy powder of the present invention contains a transition metal element homogenously compulsorily dissolved as a solid solution in a tungsten grating. Accordingly, the tungsten alloy powder may be widely used, as an alloy powder in which a portion of the tungsten is substituted by a transition metal element, for resource saving of tungsten such as tungsten carbide materials for cemented carbides. For example, the tungsten alloy powder of the present invention forms tungsten carbide, in a similar manner to that of tungsten powder can realize the preparation of cemented carbide sintered with bonded Co.

BRIEF DESCRIPTION OF DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is an image illustrating EPMA observation results of tungsten carbide including a metal phase, for the material of the present invention of Sample No. 23. (a) is an SEM image in which a white part represents a WC skeleton and a black part represents a domain composed of a Co metal. (b) represents an X-ray image of W and shows formation of a WC skeleton. (c) represents an X-ray image of Co and shows formation of a Co domain in a WC skeleton. (d) represents an X-ray image of C and shows formation of a WC skeleton.

FIG. 2 is an image illustrating EPMA observation results of tungsten carbide including a metal phase, for the material of the present invention of Sample No. 34. (a) is an SEM image in which a white part is a WC skeleton and a black part is a domain composed of a Fe—Mn solid solution. (b) represents an X-ray image of W and shows formation of a WC skeleton. (c) represents an X-ray image of Fe and shows formation of a Fe—Mn solid solution domain. (d) is an X-ray image of Co in which the bonded Co is partially distributed in the Fe—Mn solid solution domain during sintering. (e) represents an X-ray image of C and shows formation of a WC skeleton. (f) represents an X-ray image of Mn and shows formation of a Fe—Mn solid solution domain. 

1. A tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula [1] prepared by using an ammonium paratungstate aqueous solution and a transition metal complex salt aqueous solution, in which at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in a tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram. M−W  Formula [1] wherein M represents one or more selected from Co, Fe, Fe—Mn and Ni.
 2. The tungsten alloy powder with a transition metal dissolved therein as a solid solution according to claim 1, represented by Formula [2]: in which cobalt is dissolved in a tungsten grating and cobalt is partially substituted by one or more selected from the group consisting of iron, manganese and nickel. Co−M1−W  Formula [2] wherein M1 represents one or more elements selected from Fe, Fe−Mn and Ni.
 3. The tungsten alloy powder with a transition metal dissolved therein as a solid solution according to claim 1, in which iron is dissolved in a tungsten grating and iron is partially substituted by one or more selected from the group consisting of cobalt, manganese and nickel. Fe−M2−W  Formula [3] wherein M2 represents one or more elements selected from Co, Mn and Ni.
 4. The tungsten ally powder with a transition metal dissolved therein as a solid solution according to either one of claim 1, wherein 40 to 10 mol % of one or more metal selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in 60 to 90 mol % of tungsten.
 5. A process for producing the transition metal dissolved tungsten powder, which comprises: mixing an ammonium paratungstate aqueous solution containing tungsten ions with an acetate aqueous solution containing at least ions of one transition metal selected from the group consisting of cobalt, iron, manganese and nickel, wherein the mixing is performed such that the tungsten ions are 60 to 90 mol % and the transition metal ions are 40 to 10 mol %, drying the mixed aqueous solution by distillation or spraying, thermally decomposing the resulting solid, followed by hydrogen thermal reduction, to prepare a transition metal-dissolved tungsten alloy powder represented by Formula [1] of M−W (wherein M represents one or more selected from Co, Fe, Mn and Ni), in which a transition metal element is dissolved.
 6. (canceled)
 7. The tungsten ally powder with a transition metal dissolved therein as a solid solution according to claim 2, wherein 40 to 10 mol % of one or more metal selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in 60 to 90 mol % of tungsten.
 8. The tungsten ally powder with a transition metal dissolved therein as a solid solution according to claim 3, wherein 40 to 10 mol % of one or more metal selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in 60 to 90 mol % of tungsten. 